On some packing lines for manufacturing packets of cigarettes, each packet produced must be marked or punched or printed with a progressive code indicating, for example, the date and/or place of manufacture.
U.S. Pat. No. 6,098,533A1 describes a conveyor for stabilizing packets of cigarettes coming off a packing machine, and on which each packet is fed along a stabilizing path and through a marking station by two opposite, facing conveyor belts, which partly engage respective opposite minor lateral surfaces of the packet; and a laser marking device at the marking station marks a progressive code on a portion of one of the minor lateral surfaces of the packet left exposed by the respective conveyor belt.
Patent Application US2001032932A1 describes the laser marking of a progressive code on the outer surface of packets of cigarettes. The packets of cigarettes are fed forward on a conveyor (preferably a vertical drying drum) fitted with grippers, which engage each packet of cigarettes, leaving exposed a marking area of the packet, on which a laser marking device, connected to the conveyor, marks the progressive code.
Patent Application EP1916188A1 describes a packet marking unit comprising: a marking conveyor for feeding the packets successively along a marking path and having a number of pockets, each for housing a respective packet; an input station; an output station; and a marking station located along the marking conveyor, between the input station and the output station, and having a laser marking device for marking a code on the outer surface of each packet on the marking conveyor.
Depending on the type of packet of cigarettes, the progressive code must be marked on an end wall or a lateral wall of each packet. In the above known laser marking units, switching the marking area from the end to the side of the packet (or vice versa) calls for changing the position of the laser marking device with respect to the conveyor feeding the packets past the device. This is due to the fact that, under current safety regulations (i.e. to reduce harm in the event of accidental contact with the laser beam), the focal area of the laser beam is very small, which means the path of the laser beam from the laser marking device emitter to the surface of the packet must always equal a given, non-adjustable distance. In other words, to switch the marking area from the end to the side of the packet (or vice versa), the position of the laser marking device with respect to the packet conveyor must be changed so that the path of the laser beam from the laser marking device emitter to the surface of the packet is always the same length.
Changing the position of the laser marking device with respect to the packet conveyor is a fairly complicated, time-consuming job, on account of the considerable size of the device and its location in an area crowded with other components, and what is more takes at least two operators, on account of the considerable weight of the device.